1. Field of the Invention
The invention relates to a fully-differential sensing device circuit, and more particularly to a fully-differential sensing device circuit for a high pass filter.
2. Description of the Related Art
The conventional high pass filter usually includes two variable gain amplifier circuits and a large size capacitor is used to be coupled between the variable gain amplifier circuits to implement a high pass filtering function.
FIG. 1 shows a conventional high pass filter. As shown in FIG. 1, the high pass filter 1 includes a first variable gain amplifier circuit 11 and a second variable gain amplifier circuit 12. A large size capacitor 13 is coupled between the first variable gain amplifier circuit 11 and the second variable gain amplifier circuit 12 to perform charge/discharge and implement the filtering function of the high pass filer 1.
Since the large size capacitor 13 must be charged and discharged with a large current, further reducing the size of the large capacitor 13 is difficult. Thus, the large size capacitor can not be integrated with the first and second variable gain amplifier circuits 11 and 12 on the same chip, which increases the volume of the high pass filter and raises costs. Thus, a circuit which can further reduce the volume of the large capacitor is highly required.